A screen member disposed at an opening section of a high-frequency heating apparatus has hitherto been roughly classified into the following two types. Namely, one type of screen member is employed in a heating apparatus having a heater to be used for heating the internal space of a heating chamber. A laminated mica plate, which is thermally stable, is hooked on a slot provided on a wall surface of the heating chamber and secured with engagement members, such as screws. Another type of screen member is a resin-made opening section screen member often seen in a single-function type of heating apparatus which does not have any heater. The screen member is attached to a wall surface of the heating chamber by utilization of elasticity (spring characteristic) of an attachment engagement section. Engagement members, such as screws, are not usually required. Adoption of the screen member of former type for a heating apparatus of single-function type has recently become mainstream, with an aim toward curtailing costs of material and molds.
In FIG. 5, reference numeral 1 designates a heating chamber, and an opening section 2 which is to act as a high-frequency radiation inlet port is provided in a right-side side wall of the heating chamber 1. Reference numeral 3 designates a magnetron which is to serve as high-frequency radiation generation means. The magnetron 3 is attached to one end of a waveguide 4 for guiding high-frequency radiation generated in the heating chamber 1. The opening section 2 is provided in the vicinity of the other end of the waveguide 4 and covered with an opening section screen body 5. If the opening section screen body 5 is not provided, lamp black or waste which would arise from food during the course of cooking will attach to the inside or end face of the opening section 2. As a result, concentration of an electric field would develop in the waveguide 4, which has a high electric field, thereby causing burning or sparking. This results in serious failures, such as smoking, inflammation, or leakage of radio waves.
FIG. 6 shows that the opening section screen member 5 is attached to a wall surface of the heating chamber by means of a flexible plastic attachment engagement section 6 and without use of screws for engagement purpose.
As shown in FIG. 7, the opening section screen member 5 is a substantially rectangular laminated mica plate having a thickness of about 0.2 to 1 mm. In the embodiment, two of four corners of the opening section screen member 5 are inserted into slots 7 provided in the wall of the heating chamber. One area of the opening section screen member 5 is fixedly attached to the wall surface of the heating chamber by means of a screw member 8 formed in the shape of a screw or clip.
FIG. 8 is a cross-sectional view of the opening section screen member 5 taken along line A-a-A′ line shown in FIG. 7. The left end of the opening section screen member 5 is inserted into the slots 7, and the right end of the same is secured with the engagement member 8.
The example has described a rectangular opening section screen member having four corners. However, in the case of a triangular opening section screen member, two or one area may be fastened, and another one area may be fixed. Alternatively, even in the case of a rectangular opening section screen member, one or three areas may be fastened, and another area may be fixed with use of an engagement member.
FIG. 6 is a configuration into which the configuration described by reference to FIG. 7 has been further rationalized. The periphery of the thin-plate, substantially rectangular opening section screen member 5 consisting of a laminated mica plate is engaged with the slots 7 formed in the wall surface of the heating chamber. No engagement members having the shape of screw or clip are used.
The opening section screen member 5 consisting of a laminated mica plate is as thin as 1 mm or less and hence has flexibility in a thickness wise direction thereof. At this time, the opening section screen member 5 has a dimension of L mm in a longitudinal direction thereof. The drawing can be utilized as a plan view of a first embodiment of the invention, which will be described later.
The related-art configuration enables reduction of engagement members, such as screws. However, warpage which would arise when the laminated mica plate is deflected remains, thereby causing slight clearance between the laminated mica plate and the wall surface of the heating chamber. FIG. 3 is a slightly exaggerated view of the clearance. Although the clearance is nominal, a substantial center of the length of the laminated mica plate attains maximum deflection with reference to the wall of the heating chamber, which is a plane surface. Hence, the clearance becomes very noticeable in terms of appearance. That clearance is prone to accumulation of oil black originating from food or food waste splashed from food, thereby causing smoke or inflammation. Moreover, when a user cleans the heating apparatus, the clearance may become a factor for prompting the user to remove the mica plate during the course of cleaning.